 Okay, this one says you are given 2.5384 grams sample of the Epsom salt that you have just analyzed, so this thing here, and an unknown quantity of inert material. So there's a bunch of stuff in this sample. Some of it doesn't react, meaning inert, okay? But some of it does, as you well know, the magnetic sulfate. Okay, the magnetic sulfate pentohydrate does. Following heating the sample, the mass has, or the sample has a mass of 2.2176 grams. What is the mass percent of Epsom salt present in the sample, okay? So it gives us a couple of numbers. Notice it says the mass total is 2.5384 grams, and then the mass after heating is going to be 2.2176 grams, okay? So from these numbers, what can we get? What should we be able to figure out? Not yet, okay? Eventually we'll be able to do that, but just from these two numbers. So what is the difference here? What is the difference? What have we lost here? The water, so what can we get out of these numbers? Mass of the water, right? The mass of the water. Is everybody okay with that? So what would the mass of the water be? I'm sure that's what you would have putt it, right? That's how many grams of water. So what should we figure out now? I'll let you guys tell me. The moles of what? The moles of water. Okay? How will we do that? The mass of the water and... Okay, so from that, what should we be able to figure out? So remember, we're looking for the mass percent of the mag sulfate pentohydrate. Look there, it's not written on my face. So then you take the mass of all of the holes. So let's figure out the number of moles of mag sulfate pentohydrate. How will we do that? Probably add the times, water five times, and then figure out the mass weight. How do we figure out the moles of mag sulfate pentohydrate? Guys, we went over this for the last hour. We added the whole atomic weight. So we... What is... There's five quarters there, so that means you have to multiply the moles of water by five. So what is that thing called? Conversion factor. Where do you get that conversion factor from? Look up there, it's not written on my face. The chemical equation, right? So what would the conversion factor be? What are the units of? Just set it. Mole. Tell me guys, moles to moles, right? Mole to moles. What do you get from the chemical equation? What are the units you get from the chemical equation guys? Do you get any other units from the chemical equation? So why should you tell me anything else? Or not tell me anything, okay? Only one unit you get from the chemical equation. One time again I'm going to tell you, okay? I'm going to tell you 10 more times, okay? What unit do you get from the chemical equation? Moles. Okay, so what do I have down here? What units do I have down there? Moles. Moles, right? So if I have moles of water and I want moles of sulfate pentahydrate, how do I figure that out? Use the chemical equation to give the conversion factor, right? And what would that conversion factor be? Don't worry, we won't post this one. Okay? What would that conversion factor be? What do we got to cancel out? How about that? Let's start that. We got to cancel out the moles of water, okay? So moles of water is going to be on the bottom, right? So how many moles of water do we have in the chemical equation? Five. Five. The magsulfate pentahydrate? One. One. Do you have the moles of the magsulfate pentahydrate? So how do I get it? From the chemical equation, okay? You guys got to remember this stuff, we got to remember, it's super-duper important, okay? There's only two things that we have learned today. The conversion factor that is molar mass and the conversion factor that is from the chemical equation. If you can't do those two things, you need to work on it, okay? Molar mass converts grams to moles. Chemical equation converts moles to moles, okay? And just because somebody else doesn't know how to do it, doesn't mean you don't know how to do it. Chemistry haters out there, okay? So if you're sitting next to a chemistry hater who's hating, you know, don't listen. Cancel that juice, you know what I'm saying? Because you got to get through this stuff. It's true. I know it sounds hilarious, you know, but it's true. People hate. You know what I'm saying? If you're going to do that, or if somebody next to you is doing that, tell them to cancel that stuff. You know, you can't hear that. You got to get through this stuff. There's only two things you learned. I know you can do this. Divide this by five and we get this number. Is that mass percent there? No. So what do we have to get from the moles to eventually get mass percent? We've got to get the mass, right? The mass. So what do we know, what conversion factor do we know that gives the mass from the moles? Yeah, what is it called? Remember two things number two things. Okay, just multiple of them like two ten point four seven point seven Four nine is that mass percent? No, that's just the mass of the mag-salt and temperature Or the percent of the entire samples. What was the weight of the entire sample? Yep, two point five three eight four. So how do I get the mass percent guys help me out? What's numbers on top? Very good, you guys are good at that. So it's just a series of steps. I know it seems like a lot, okay? So this is exactly how to do the other two problems on the Pre-lap you just substitute instead of water for carbon dioxide in one and instead of mag-sulfate use copper-2-sulfate